Method of producing fire retardance in a prefinished panel

ABSTRACT

A METHOD OF PRODUCING FIRE RETARDANCE IN A PREFINISHED PANEL. A PANEL IS IMPREGNATED IN A REGION DIRECTLY ADJACENT ITS FACE WITH A FIRE RETARDANT CHEMICAL SOLUTION AT AN ELEVATED TEMPERATURE. AFTER SUBSEQUENT CALENDERING AND DRYING, TO PRODUCE A DENSE IMPREGNATED LAYER EXTENDING OVER THE FACE OF THE PANEL, THE FINISH IS APPLIED, WITH SUCH LAYER THEN ACTING AS A FIRE RETARDANT BARRIER IN THE PANEL UNDER THE FINISH.

C. E. MYERS Aug. 8, 1972 METHOD OF PRODUCING FIRE RETARDANCE IN A PREFINISHED PANEL Filed Oct. 28, 1969 Fig 2.

United States Patent Ofice Patented Aug. 8, 1972 r 3,682,675 METHOD OF PRODUCING FIRE RETARDANCE IN A PREFINISHED PANEL Clifford E. Myers, Forest Grove, Oreg., assignor to The Welsh Corporation, Longview, Wash. Filed Oct. 28, 1969, Ser. No. 871,915 Int. Cl. B44d 1/14; C091: 3/28 U.S. Cl. 1178 6 Claims ABSTRACT OF THE DISCLOSURE This invention concerns the production of prefinished panels, and more particularly the production of such panels having a fire-retardant property.

According to this invention, it has beendiscovered that prefinished panels, such as plywood panels, are readily given a fire-retardant property through the expedient of impregnating the panel through its faceover a region directly adjacent its face with a fire-retardant chemical, and then roll pressingor calendering the panel to produce compaction of this impregnated region with the production of a dense, impregnated surface layer extending over the face of the panel. As the result of the calendering step, and 'because of the presence of the fire-retardant chemical within the cells of the wood, a smoothing of theface of the panel is produced which promotes the production of a lustrous, smooth finish in the panel as finally finished. Thus, various coatings to produce such a finish may be applied directly over the face of the panel without an intermediate sanding step, or if sanding is performed, such need only be an easily performed light sanding with minimum removal of material. The compacting of the impregnated region of the panel also contributes to greater fire retardance, probably best explainable by reason of the reduction of voids which occurs by reason of densifying the wood. In the final panel, the hardened surface layer forms a fire-retardant barrier directly underlying the finish which has been applied. a

The impregnation of the wood is preferably performed using a chemical solution which is at an elevated temperature; This promotes the use of a more concentrated solution. Furthermore, with the Wood immersed in such a solution during the impregnation part of the process, such elevated temperature contributes to increasing the plasticity of the wood, whereby it is more easilysmoothed and densified during the calendering step. I p

The calendering is preferably done with a cooled roller. As a consequence, during the calendering or roll pressing, the chemical which has impregnated the wool is cooled, with this serving to initiate setting or hardening of the chemical. As the chemical sets, it tends to retain the wood in the impregnated layer in its compacted or. densified condition. v

Calendering of the panel also preferably is performed with wiping of excess solution on the face of the panel from off the panel. Such Wiping may be advantageously done by rotating the roll which is used to roll press the wood against the direction of travel of the panel as it moves by the roll. This wiping promotes faster drying of the panel when it is subsequently subjected to drying. Also, it contributes to the production of a more uniformly colored panel, in that concentrations of chemical in localized face regions of the panel are eliminated. This is very important in producing'clear and semi-opaque finishes on a panel when the natural appearance of the wood is retained to a degree on the face of a panel.

Both clear and colored finishes are possible utilizing the invention. The calendering may be done with smoothsurfaced rolls, or with embossment-type rolls when it is desired to emboss a pattern on the face of a panel. An embossing roller might be used, for instance, when it is desired to emboss into the face of the panel a simulated grain pattern, to complement or take the place of what is otherwise an indistinct grain on the face of the-panel.

Other various features and objects of the invention will become more fully apparent upon reading the following detailed description, which is to be taken in conjunction with the accompanying drawings wherein:

FIG. lillustrates, in somewhat simplified form, apparatus such as that which might be used in impregnating the panel with fire-retardant chemical; and

FIG. 2 illustrates the calendering of the panel, which functions to compact the impregnated region of the panel to obtain a hardened dense layer extending over its face.

Generally describing the invention, the panel is first processed to impregnate a region of the panel directly adjacent its face with a fire-retardant solution. As will be appreciated by those skilled in the art, such impregnation of the panel through its face may be done in a number of different ways. I prefer to accomplish this step by immersing the panel in a hot solution of fire-retardant chemical, and then subjecting the solution, and the panel which is immersed therein, to compressional wave energy in a frequency ranging from sonic to ultrasonic, to promote acceptance by the wood of the chemical solution.

The solution, during the impregnation, may be at an elevated temperature, with such preferably having a temperature ranging from about F. to the boiling point of the solution. With a hot solution, impregnation of the wood proceeds more rapidly. Furthermore, solutions of relatively high chemical concentration canbe utilized in the impregnation step. Additionally, the wood, by such hot solution, is warmed and rendered more plastic, which facilitates the compacting of the wood which occurs as a later part of the process.

Various frequencies can be employed for the compressional wave energy, from sonic to ultrasonic frequencies. The wave energy is produced using a transducer, for instance, that con'vert's electrical energy fed to it at a certain frequency into mechanical vibrations of a diaphragm or plate in the transducer. Various forms of transducers may be employed, including natural or artificially polarized piezoelectrics, electrostrictive or magnetostrictive.

. As the result of the impregnation step, and considering, for instance, the impregnation of a three-ply plywood panel, ordinarily chemical impregnation will occur inwardly from opposite faces and proceed usually to about the glue-lines bonding the outer face sheets of the panel to the core. Impregnation of the core is difficult because of the presence of these glue-lines. However, according 'in the panel are exposed in the immersion step directly to the impregnating solution. Further, since V-grooves usually are prepared to a depth reaching approximately the, glue-line which bonds the face veneer of the panel in place, and should such glue-line be inadvertently cut, this procedure assures that any core layer exposed by such cutting be fully impregnated-the cut region.

Exemplifying solutions which have been employed in the impregnation to obtain fire-retardance are aqueous solutions of diammonium phosphate, borax, and mixtures of the two. The solutions ordinarily are prepared as concentrated solutions, at the particular temperature used for the impregnation step.

In FIG. 1, apparatus such as might be utilized-for the impregnation of the panel is depicted in simplified form. Such includes ;a tank 10, with transducers 12, 14 and 16 provided at the base, and on opposite ends of the tank. A panel, such as that shown at 18, is immersed in solution carried in the tank. Typically the panel is subjected to a presoaking period, followed by a period where compressional wave energy is directed inwardly into the tank from the transducers. After such treatment, the :panel may be subjected to another soaking periodbefore its removal.

On removal of the panel from the tank, the same may be passed between a pair of calendering rolls, such as'those shown at 26, 28. These may be made of rubber, of relatively hard durometer. Alternatively, smooth metal. surfaced rolls may be employed. To produce a flat-facedip'anel, the rolls are cylindrically surfaced. Where an embossed design is desired on the face of the panel, theroll which contacts the face may be provided with ridges corresponding to the design which is. to be embossed. Using either type of roll, the face of the panelwhere contacted by the roll is smoothed, and compaction of the .wood immediately adjacent the face is produced. With -the.usual type of panel, the pressure of the roll where it makes contact with the panel is selected to be within the range of 50 to 200 pounds per lineal inch of roll. With lower pressures, there is less than the desired amount of compacting and densifying of surface regions in the panel and higher pressures introduce processing difficulties.

To promote wiping of the panel, roll 26 contactingthe face of the panel (and roll 28 contacting theback of the panel if desired) is rotated against the direction of travel of the panel between rolls 26, 28. Movement of the panel in the desired direction may be produced through providing drive rollers, such as those shown at 29, which rotate in the opposite direction. With wiping, excess solution is removed from the faces of the panel, which is to say that accumulations of solution not carried within the wood itself are removed. By reason of such wiping, and after drying, the panel faces are free of streaks formed by concentrations of crystallized chemical carried on thesurface of the panel. A panel is produced which usually resembles an untreated panel, save for a slight change'in overall color tone. Of course, if the roll has other a smooth surface, the roll is rotated in the direction that the panel moves. p

Preferably, the panels are transported to the rolls immediately on leaving impregnation tank 10, andwhile still essentially at the temperature of the solution in the tank. The rolls themselves are cooled, as by circulating water through their interiors, whereby their surfaces aremaintained usually below about 100 F. and preferably in. the range of 5080 F. By cooling the rolls, there is cooling of surface regions of the panel as it is calendered, which cooling initiates the setting up or hardening of the chemical impregnant. By reason of this action, aninte'rnal bond its moisture content, to a level comparable to natural equilibrium conditions, i.e., about percent (based on the dry weight of wood). In the drying, a temperature preferably not exceeding 135 F. is employed for the air temby the calendering rolls.-

perature. It is desired to effect water removal with. an

of the smoothened condition of the panel face as produced In preparing the finish on the panel, the usual steps employed in making such a finish may be utilized. Thus, a base coat may first be applied, using, for example, a water base emulsion, or a lacquer type coating composition. Over this a color coat may be applied, using a colored lacquer type coating composition. Subsequently a seal coat (to give buildup to the finish) may be applied, followed by the application of a top coat which gives the panel a hard smooth finish.

In some instances it may be desirable to roll press the panel after the application of the base coat. Such might be done, for instance, whenan embossed design is prepared on the panel face. When'this procedure is utilized, the panel has already been subjected to drying, and the wood in the panel adjacent its faces is hard and not as plastic as the wood in such regions of the panel at the time the panel leaves tank 10 and immediately after impregnationl With this type of roll pressing, pressures up to'lOOO lbs. per lineal inch may be used, and the roll is rotated'with the direction of travel of the work. Difiiculties would be encountered in moving the work if roll rotation were against the travel of the work using these high pressures.

Describing the production of a particular panel, a solution of fire-retardant chemical was prepared by mixing diammonium phosphate and borax, at the rate ofseven pounds of diammonium phosphate and sevenpounds-anhydrous borax in one gallon of water. The water had'a temperature of 200 F. At such temperature, substantially all the phosphate and borax entered into solution. Tank 10 was filled with such solution, and a three-ply, At-inch plywood panel, made of lauan and predried to about 9 percent moisture/content, was immersed in such tank. The panel was subjected to a preliminary soak of one minute. This was followed 'by energizing the transducers, using a power inputto each of the two end transducers 14, 16 of fifteen hundred watts, and to the bottom transducer 12 of three thousandwatts. The transducers operated at a frequency of 21 kilocycles. The tank was subjected to compressional wave energy by operation of the transducers fora period of one minute; Subsequently, the panel was subjected to another soaking period of one minute.

The panel which had been softened by the hot water or solvent of the solution was then removed from the tank, and passed between calendering rolls. Each roll exerteda pressure of about pounds per lineal inch on the face' 'oflthe panel that the roll contactedJOn passing through the rolls, the panel was reduced in thickness about .025' inch;with compacting of regions of the panel adjacent opposite faces of the panel. Therolls were cooled to 75 F.'by circulating cool -water through them. The rolls on squeezingag'ainst opposite faces of the panel, served to wipe err excess chemical solution on the faces of the panel. The cooling action of the rolls initiated setting of the fire-retardant chemical, giving the panclffaces atacky quality.

After calendering, the panel was dried by circulating air at approximately100 F. over the panel. Such drying was continued until the'moisture content of the panel was reduced to about lO percent. I

The panel after such treatment had smooth hardened outer faces, and a uniform color which was only slightly darker than the panel without treatment. The calendering produced hardened layers over opposite panel faces which, by observation, appeared to be approximately ,5 inch .thick.

ing a seal coat was prepared from an alkyl resin coating composition comprising 30 percent alkyl resin carried in a toluene-methyl ethyl ketone solvent. Over the seal coat a top coat was applied, from a coating composition comprising 50 percent alkyl resin carried in butyl acetate solvent.

Specimens of panels so prepared were subjected to a flame spread test (ASTM Designation E84-67) to determine their burning characteristics, and these gave a flame spread classification or index of 18. The retention of chemical in such specimens, determined by weighing samples of uniform moisture content before and after treatment, was determined to be within the range of 2%. to 3 pounds per cubic foot.

The finished panel had a glossy lustrous appearance, even in the absence of a sanding of the face after calendering. The panel faces initially had been rough sanded only, to have the conditions that such panel faces normally have on shipment from a Philippine supplier.

If a panel is given a burnishing treatment or light sanding after impregnation and drying, an exceptionally deep and lustrous gloss is obtainable in the panel when finally finished. With face regions of the panel impregnated with fire retardant chemical, such chemical was noted to function as a filling medium and thus contributes significantly to the obtaining of a deep glossy finish.

While a particular practice of the invention has been described, obviously variations and changes are possible. It is intended to cover all such modifications and variations as would be apparent to one skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. A method of producing a prefinished wood panel having fire retardance which consists of impregnating a region of a panel directly adjacent its face with an aqueous solution of fire-retardant chemical whereby such chemical is carried into such face region, said impregnation of the panel being performed by immersing a wood panel in the aqueous solution of chemical at a temperature above about 125 F. with the wood in the panel being softened during such immersion, thereafter roll pressing the face of the panel while it is essentially at the temperature of said solution to compact the impregnated face region and to form a compacted and dense impregnated layer extending over the face of the panel, said roll pressing being performed after withdrawing the panel from the solution and together with wiping of excess solution carried on the face of the panel from off its face, and afterwards applying a finish coating over said face of the panel to produce a coated panel where said compacted and dense impregnated layer constitutes a fire-retardant barrier underneath said finish coating.

2. The method of claim 1, wherein the roll pressing is performed with a roll having a surface temperature below the temperature of the solution, whereby cooling is performed with roll pressing.

3. The method of claim 1, wherein the fire-retardant chemical sets when reduced in temperature from the temperature it possesses during the impregnation step, and wherein said roll has a surface temperature which is efiective to produce such setting of said chemical.

4. The method of claim 1, wherein the panel is air dried after wiping off of the excess solution carried on the face of the panel, with air at a temperature of not more than 135 F. '4

5. The method of claim 1, wherein V-grooves are prepared in the panel face extending over its face and said grooves are prepared before impregnating with fire-retardant chemical.

6. The method of producing fire retardance in a prefinished panel consisting of immersing the panel in an aqueous solution of fire-retardant chemical, said solution having a temperature ranging from F. to boiling temperature, during such immersion impregnating a region of the panel directly adjacent its face with said solution, producing softening of the wood in the panel with such immersion in solution, removing the panel from the solution and then roll pressing its face with a roll having a surface temperature below the temperature of the solution to efiect compaction of the impregnated face region to produce a dense impregnated layer, wiping excess solution carried on the face of the panel from 01f the face of the panel, cooling the face of the panel, air drying the panel with air at a temperature not exceeding F., and subsequently applying a finish coating over the face of the panel to produce a coated panel where said dense impregnated layer constitutes a fire-retardant barrier between the finish coating and the remainder of the panel.

References Cited UNITED STATES PATENTS 107,428 9/1870 Wheeler 11757 X 446,962 2/1891 Bryce 117-57 X 1,610,233 12/1926 Abbott 11757 X 1,766,606 6/1930 Coolidge 117-147 X 2,674,543 4/ 4 KhndZorian-Iablokoff l17-148 X 2,829,980 4/1958 Redd 117-1 19.2 X 3,106,485 10/1963 Guillet et al 117--119.2 3,128,199 4/ 1964 Foster 117--72 X 3,139,372 6/1964 Elliott 1l765.2 X 3,218,191 1l/1965 Domanski 11772 3,219,473 11/1965 Dimond l1765.2 X 3,297,470 1/ 1967 Martel 117-54 FOREIGN PATENTS 223,402 9/ 1957 Australia 117--65.2 885,686 12/1961 Great Britain 117-113 10,397 11/ 1968 Japan 117-65 OTHER REFERENCES Gralen et al., Journal of Polymer Science, Treatment of Wood vol. VI, No. 4, pp. 503-507.

WILLIAM D. MAR-TIN, Primary Examiner H. J. GWINNELL, Assistant Examiner US. Cl. X.R.

11765.2, 72, 116, 119.2, 138, 147 Dig. 8 

